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+~~ Licensed under the Apache License, Version 2.0 (the "License");
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+~~ you may not use this file except in compliance with the License.
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+~~ You may obtain a copy of the License at
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+~~
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+~~ http://www.apache.org/licenses/LICENSE-2.0
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+~~
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+~~ Unless required by applicable law or agreed to in writing, software
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+~~ distributed under the License is distributed on an "AS IS" BASIS,
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+~~ WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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+~~ See the License for the specific language governing permissions and
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+~~ limitations under the License. See accompanying LICENSE file.
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+
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+ ---
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+ Hadoop Distributed File System-${project.version} - Support for Multi-Homed Networks
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+ ---
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+ ---
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+ ${maven.build.timestamp}
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+
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+HDFS Support for Multihomed Networks
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+
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+ This document is targetted to cluster administrators deploying <<<HDFS>>> in
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+ multihomed networks. Similar support for <<<YARN>>>/<<<MapReduce>>> is
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+ work in progress and will be documented when available.
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+
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+%{toc|section=1|fromDepth=0}
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+
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+* Multihoming Background
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+
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+ In multihomed networks the cluster nodes are connected to more than one
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+ network interface. There could be multiple reasons for doing so.
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+
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+ [[1]] <<Security>>: Security requirements may dictate that intra-cluster
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+ traffic be confined to a different network than the network used to
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+ transfer data in and out of the cluster.
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+
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+ [[2]] <<Performance>>: Intra-cluster traffic may use one or more high bandwidth
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+ interconnects like Fiber Channel, Infiniband or 10GbE.
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+
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+ [[3]] <<Failover/Redundancy>>: The nodes may have multiple network adapters
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+ connected to a single network to handle network adapter failure.
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+
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+
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+ Note that NIC Bonding (also known as NIC Teaming or Link
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+ Aggregation) is a related but separate topic. The following settings
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+ are usually not applicable to a NIC bonding configuration which handles
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+ multiplexing and failover transparently while presenting a single 'logical
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+ network' to applications.
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+
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+* Fixing Hadoop Issues In Multihomed Environments
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+
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+** Ensuring HDFS Daemons Bind All Interfaces
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+
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+ By default <<<HDFS>>> endpoints are specified as either hostnames or IP addresses.
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+ In either case <<<HDFS>>> daemons will bind to a single IP address making
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+ the daemons unreachable from other networks.
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+
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+ The solution is to have separate setting for server endpoints to force binding
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+ the wildcard IP address <<<INADDR_ANY>>> i.e. <<<0.0.0.0>>>. Do NOT supply a port
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+ number with any of these settings.
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+
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+----
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+<property>
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+ <name>dfs.namenode.rpc-bind-host</name>
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+ <value>0.0.0.0</value>
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+ <description>
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+ The actual address the RPC server will bind to. If this optional address is
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+ set, it overrides only the hostname portion of dfs.namenode.rpc-address.
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+ It can also be specified per name node or name service for HA/Federation.
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+ This is useful for making the name node listen on all interfaces by
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+ setting it to 0.0.0.0.
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+ </description>
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+</property>
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+
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+<property>
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+ <name>dfs.namenode.servicerpc-bind-host</name>
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+ <value>0.0.0.0</value>
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+ <description>
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+ The actual address the service RPC server will bind to. If this optional address is
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+ set, it overrides only the hostname portion of dfs.namenode.servicerpc-address.
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+ It can also be specified per name node or name service for HA/Federation.
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+ This is useful for making the name node listen on all interfaces by
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+ setting it to 0.0.0.0.
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+ </description>
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+</property>
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+
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+<property>
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+ <name>dfs.namenode.http-bind-host</name>
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+ <value>0.0.0.0</value>
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+ <description>
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+ The actual adress the HTTP server will bind to. If this optional address
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+ is set, it overrides only the hostname portion of dfs.namenode.http-address.
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+ It can also be specified per name node or name service for HA/Federation.
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+ This is useful for making the name node HTTP server listen on all
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+ interfaces by setting it to 0.0.0.0.
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+ </description>
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+</property>
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+
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+<property>
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+ <name>dfs.namenode.https-bind-host</name>
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+ <value>0.0.0.0</value>
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+ <description>
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+ The actual adress the HTTPS server will bind to. If this optional address
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+ is set, it overrides only the hostname portion of dfs.namenode.https-address.
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+ It can also be specified per name node or name service for HA/Federation.
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+ This is useful for making the name node HTTPS server listen on all
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+ interfaces by setting it to 0.0.0.0.
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+ </description>
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+</property>
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+----
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+
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+** Clients use Hostnames when connecting to DataNodes
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+
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+ By default <<<HDFS>>> clients connect to DataNodes using the IP address
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+ provided by the NameNode. Depending on the network configuration this
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+ IP address may be unreachable by the clients. The fix is letting clients perform
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+ their own DNS resolution of the DataNode hostname. The following setting
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+ enables this behavior.
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+
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+----
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+<property>
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+ <name>dfs.client.use.datanode.hostname</name>
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+ <value>true</value>
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+ <description>Whether clients should use datanode hostnames when
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+ connecting to datanodes.
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+ </description>
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+</property>
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+----
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+
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+** DataNodes use HostNames when connecting to other DataNodes
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+
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+ Rarely, the NameNode-resolved IP address for a DataNode may be unreachable
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+ from other DataNodes. The fix is to force DataNodes to perform their own
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+ DNS resolution for inter-DataNode connections. The following setting enables
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+ this behavior.
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+
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+----
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+<property>
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+ <name>dfs.datanode.use.datanode.hostname</name>
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+ <value>true</value>
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+ <description>Whether datanodes should use datanode hostnames when
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+ connecting to other datanodes for data transfer.
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+ </description>
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+</property>
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+----
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+
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Arpit Agarwal